Reptiles vs Mammals: A Beastly Brawl!

Are you more interested in a furry friend or a scaly sidekick? Having trouble deciding? Let’s meet these two animals classes and see which one has the stuff to make it to the top of the Eyewire leaderboard!


Reptiles arose 300 million years ago during the Carboniferous period of the late Paleozoic Era. The Paleozoic Era was followed by the Mesozoic Era, where reptiles really thrived. The Mesozoic Era was also known as the “Age of Reptiles,” with dinosaurs and the ancestors of the crocodilians being the dominant land vertebrates.

If you like your animals supersized, reptiles might be the ones for you. Today’s reptiles range from thumb-sized to crocodile, but back in the day select dinosaurs, like the argentinosaurus huinculensis were some of the largest land animals to have ever lived!

Reptiles are categorized as animals that have scales or scutes (bony protective plates), lay land-based hard-shelled eggs, and possess ectothermic metabolisms (cold-blooded). Reptiles have an easy job of parenting – they lay their eggs in a simple nest and then skedaddle! Young reptilian hatchlings can glide, walk, and/or swim within hours of birth.

There are 4 orders of reptilia: Testudines (turtles), Rhynchocephalia (2 species of New Zealand tuatara are the only survivors of this order), Squamata (the current largest order consisting of lizards, snakes and amphisbaenians), and Crocodilia (alligators, caimans, crocodiles and gharials).


If you’re super trendy and only accept the latest fashions and newest styles, then mammals may be the animal class for you.

The modern Cenozoic Era (meaning “recent life”), is also called the “Age of Mammals.” Beginning 65 million years ago this era followed the Cretaceous-Paleogene extinction event that wiped out the non-avian dinosaurs.

We’ve got some pretty impressively large mammals today such as hippos and giraffes, but before the Quaternary extinction event that wiped out a lot of prehistoric megafauna, many other large mammals roamed the earth. The largest known mammal was the Paraceratherium, a hornless rhinoceros that was estimated to stand 4.8 meters (15.7 feet) tall, and was 7.4 meters (24.3 feet) in length. Other extinct megafauna include mammoths, mastodons, ground sloths, and dire wolves.

Despite the many mammal extinctions that happened through the modern era, overall mammals flourished and diversified during the Cenozoic Era. While the megafauna may have had a bit of a struggle, don’t count out the little guy – rodents, bats, and shrews make up over 70% today’s 6400+ mammalian species! Fun!

So what are mammals? These cuddly cuties are endothermic (warm-blooded) vertebrates with hair or fur. They are unique from other species in that they produces milk to nourish their young, and almost all give birth to live young (platypuses and echidnas being the egg-laying exceptions). Because their young are reliant on them for sustenance in early years, mammals  must also care for their young for at least a few weeks (and sometimes many years, as human parents are well aware!). Another interesting physical attribute that defines the mammal class is the thoracic diaphragm – a sheet of muscle that divides the thoracic cavity from the abdominal cavity and assists with breathing.

Scales or fur? ecto or endo? Eggs or no eggs? Choose your side and let the competition begin! Join us 3/8 at 11 AM ET for 48 hours of animal madness!

Art by Daniela Gamba